It won't be BW since we have exactly ONE female superhero in the MCU (SW makes two, still not enough). It wont be Hawkeye since he's gotten the least amount of screentime/development, so killing him off (and wasting Jeremy Renner) would be pointless and lazy. I'm guessing that Nick Fury may die. That way, Maria Hill would become Director of SHIELD and add new complications in the MCU. I could also potentially see IM dying.